1. Field of the Invention
The invention relates to a catalyst containing oxides of at least the metals vanadium and molybdenum and a method of producing the same.
2. Description of the Related Art
Such catalysts have become increasingly important for reducing nitrogen oxides in flue gases in the presence of a reducing agent, among other purposes. To this end, the flue gases containing nitrogen oxides are enriched with a reducing agent, typically ammonia or carbon monoxide, and moved past the catalytically active surfaces. In this process, the nitrogen oxides are converted into nitrogen and water vapor, with simultaneous oxidation of the ammonia. Catalysts that contain oxides of one or more of the metals titanium, vanadium, molybdenum and tungsten are generally used for this purpose.
When such catalysts are used in flue gases containing nitrogen oxides, it has been found that they lose their catalytic activity over time. That decrease in catalytic activity proceeds faster with higher proportions of arsenic in the flue gases. When such catalysts are used in a flue gas flow upstream of a flue gas scrubber, particularly when ash recirculation into a melting chamber is provided, such catalysts deactivate especially quickly because of a process-dictated concentration of catalyst poisons, such as arsenous oxide.
In order to avert the decrease in catalytic activity as much as possible, various mixtures of catalytically active components have already been studied. However, it was only possible to slightly improve the course of deactivation.